Merge tag 'spi-fix-v5.14-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/brooni...

[linux-2.6-microblaze.git] / kernel / sched / deadline.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Deadline Scheduling Class (SCHED_DEADLINE)
 *
 * Earliest Deadline First (EDF) + Constant Bandwidth Server (CBS).
 *
 * Tasks that periodically executes their instances for less than their
 * runtime won't miss any of their deadlines.
 * Tasks that are not periodic or sporadic or that tries to execute more
 * than their reserved bandwidth will be slowed down (and may potentially
 * miss some of their deadlines), and won't affect any other task.
 *
 * Copyright (C) 2012 Dario Faggioli <raistlin@linux.it>,
 *                    Juri Lelli <juri.lelli@gmail.com>,
 *                    Michael Trimarchi <michael@amarulasolutions.com>,
 *                    Fabio Checconi <fchecconi@gmail.com>
 */
#include "sched.h"
#include "pelt.h"

struct dl_bandwidth def_dl_bandwidth;

static inline struct task_struct *dl_task_of(struct sched_dl_entity *dl_se)
{
        return container_of(dl_se, struct task_struct, dl);
}

static inline struct rq *rq_of_dl_rq(struct dl_rq *dl_rq)
{
        return container_of(dl_rq, struct rq, dl);
}

static inline struct dl_rq *dl_rq_of_se(struct sched_dl_entity *dl_se)
{
        struct task_struct *p = dl_task_of(dl_se);
        struct rq *rq = task_rq(p);

        return &rq->dl;
}

static inline int on_dl_rq(struct sched_dl_entity *dl_se)
{
        return !RB_EMPTY_NODE(&dl_se->rb_node);
}

#ifdef CONFIG_RT_MUTEXES
static inline struct sched_dl_entity *pi_of(struct sched_dl_entity *dl_se)
{
        return dl_se->pi_se;
}

static inline bool is_dl_boosted(struct sched_dl_entity *dl_se)
{
        return pi_of(dl_se) != dl_se;
}
#else
static inline struct sched_dl_entity *pi_of(struct sched_dl_entity *dl_se)
{
        return dl_se;
}

static inline bool is_dl_boosted(struct sched_dl_entity *dl_se)
{
        return false;
}
#endif

#ifdef CONFIG_SMP
static inline struct dl_bw *dl_bw_of(int i)
{
        RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held(),
                         "sched RCU must be held");
        return &cpu_rq(i)->rd->dl_bw;
}

static inline int dl_bw_cpus(int i)
{
        struct root_domain *rd = cpu_rq(i)->rd;
        int cpus;

        RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held(),
                         "sched RCU must be held");

        if (cpumask_subset(rd->span, cpu_active_mask))
                return cpumask_weight(rd->span);

        cpus = 0;

        for_each_cpu_and(i, rd->span, cpu_active_mask)
                cpus++;

        return cpus;
}

static inline unsigned long __dl_bw_capacity(int i)
{
        struct root_domain *rd = cpu_rq(i)->rd;
        unsigned long cap = 0;

        RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held(),
                         "sched RCU must be held");

        for_each_cpu_and(i, rd->span, cpu_active_mask)
                cap += capacity_orig_of(i);

        return cap;
}

/*
 * XXX Fix: If 'rq->rd == def_root_domain' perform AC against capacity
 * of the CPU the task is running on rather rd's \Sum CPU capacity.
 */
static inline unsigned long dl_bw_capacity(int i)
{
        if (!static_branch_unlikely(&sched_asym_cpucapacity) &&
            capacity_orig_of(i) == SCHED_CAPACITY_SCALE) {
                return dl_bw_cpus(i) << SCHED_CAPACITY_SHIFT;
        } else {
                return __dl_bw_capacity(i);
        }
}

static inline bool dl_bw_visited(int cpu, u64 gen)
{
        struct root_domain *rd = cpu_rq(cpu)->rd;

        if (rd->visit_gen == gen)
                return true;

        rd->visit_gen = gen;
        return false;
}
#else
static inline struct dl_bw *dl_bw_of(int i)
{
        return &cpu_rq(i)->dl.dl_bw;
}

static inline int dl_bw_cpus(int i)
{
        return 1;
}

static inline unsigned long dl_bw_capacity(int i)
{
        return SCHED_CAPACITY_SCALE;
}

static inline bool dl_bw_visited(int cpu, u64 gen)
{
        return false;
}
#endif

static inline
void __add_running_bw(u64 dl_bw, struct dl_rq *dl_rq)
{
        u64 old = dl_rq->running_bw;

        lockdep_assert_rq_held(rq_of_dl_rq(dl_rq));
        dl_rq->running_bw += dl_bw;
        SCHED_WARN_ON(dl_rq->running_bw < old); /* overflow */
        SCHED_WARN_ON(dl_rq->running_bw > dl_rq->this_bw);
        /* kick cpufreq (see the comment in kernel/sched/sched.h). */
        cpufreq_update_util(rq_of_dl_rq(dl_rq), 0);
}

static inline
void __sub_running_bw(u64 dl_bw, struct dl_rq *dl_rq)
{
        u64 old = dl_rq->running_bw;

        lockdep_assert_rq_held(rq_of_dl_rq(dl_rq));
        dl_rq->running_bw -= dl_bw;
        SCHED_WARN_ON(dl_rq->running_bw > old); /* underflow */
        if (dl_rq->running_bw > old)
                dl_rq->running_bw = 0;
        /* kick cpufreq (see the comment in kernel/sched/sched.h). */
        cpufreq_update_util(rq_of_dl_rq(dl_rq), 0);
}

static inline
void __add_rq_bw(u64 dl_bw, struct dl_rq *dl_rq)
{
        u64 old = dl_rq->this_bw;

        lockdep_assert_rq_held(rq_of_dl_rq(dl_rq));
        dl_rq->this_bw += dl_bw;
        SCHED_WARN_ON(dl_rq->this_bw < old); /* overflow */
}

static inline
void __sub_rq_bw(u64 dl_bw, struct dl_rq *dl_rq)
{
        u64 old = dl_rq->this_bw;

        lockdep_assert_rq_held(rq_of_dl_rq(dl_rq));
        dl_rq->this_bw -= dl_bw;
        SCHED_WARN_ON(dl_rq->this_bw > old); /* underflow */
        if (dl_rq->this_bw > old)
                dl_rq->this_bw = 0;
        SCHED_WARN_ON(dl_rq->running_bw > dl_rq->this_bw);
}

static inline
void add_rq_bw(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
        if (!dl_entity_is_special(dl_se))
                __add_rq_bw(dl_se->dl_bw, dl_rq);
}

static inline
void sub_rq_bw(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
        if (!dl_entity_is_special(dl_se))
                __sub_rq_bw(dl_se->dl_bw, dl_rq);
}

static inline
void add_running_bw(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
        if (!dl_entity_is_special(dl_se))
                __add_running_bw(dl_se->dl_bw, dl_rq);
}

static inline
void sub_running_bw(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
        if (!dl_entity_is_special(dl_se))
                __sub_running_bw(dl_se->dl_bw, dl_rq);
}

static void dl_change_utilization(struct task_struct *p, u64 new_bw)
{
        struct rq *rq;

        BUG_ON(p->dl.flags & SCHED_FLAG_SUGOV);

        if (task_on_rq_queued(p))
                return;

        rq = task_rq(p);
        if (p->dl.dl_non_contending) {
                sub_running_bw(&p->dl, &rq->dl);
                p->dl.dl_non_contending = 0;
                /*
                 * If the timer handler is currently running and the
                 * timer cannot be canceled, inactive_task_timer()
                 * will see that dl_not_contending is not set, and
                 * will not touch the rq's active utilization,
                 * so we are still safe.
                 */
                if (hrtimer_try_to_cancel(&p->dl.inactive_timer) == 1)
                        put_task_struct(p);
        }
        __sub_rq_bw(p->dl.dl_bw, &rq->dl);
        __add_rq_bw(new_bw, &rq->dl);
}

/*
 * The utilization of a task cannot be immediately removed from
 * the rq active utilization (running_bw) when the task blocks.
 * Instead, we have to wait for the so called "0-lag time".
 *
 * If a task blocks before the "0-lag time", a timer (the inactive
 * timer) is armed, and running_bw is decreased when the timer
 * fires.
 *
 * If the task wakes up again before the inactive timer fires,
 * the timer is canceled, whereas if the task wakes up after the
 * inactive timer fired (and running_bw has been decreased) the
 * task's utilization has to be added to running_bw again.
 * A flag in the deadline scheduling entity (dl_non_contending)
 * is used to avoid race conditions between the inactive timer handler
 * and task wakeups.
 *
 * The following diagram shows how running_bw is updated. A task is
 * "ACTIVE" when its utilization contributes to running_bw; an
 * "ACTIVE contending" task is in the TASK_RUNNING state, while an
 * "ACTIVE non contending" task is a blocked task for which the "0-lag time"
 * has not passed yet. An "INACTIVE" task is a task for which the "0-lag"
 * time already passed, which does not contribute to running_bw anymore.
 *                              +------------------+
 *             wakeup           |    ACTIVE        |
 *          +------------------>+   contending     |
 *          | add_running_bw    |                  |
 *          |                   +----+------+------+
 *          |                        |      ^
 *          |                dequeue |      |
 * +--------+-------+                |      |
 * |                |   t >= 0-lag   |      | wakeup
 * |    INACTIVE    |<---------------+      |
 * |                | sub_running_bw |      |
 * +--------+-------+                |      |
 *          ^                        |      |
 *          |              t < 0-lag |      |
 *          |                        |      |
 *          |                        V      |
 *          |                   +----+------+------+
 *          | sub_running_bw    |    ACTIVE        |
 *          +-------------------+                  |
 *            inactive timer    |  non contending  |
 *            fired             +------------------+
 *
 * The task_non_contending() function is invoked when a task
 * blocks, and checks if the 0-lag time already passed or
 * not (in the first case, it directly updates running_bw;
 * in the second case, it arms the inactive timer).
 *
 * The task_contending() function is invoked when a task wakes
 * up, and checks if the task is still in the "ACTIVE non contending"
 * state or not (in the second case, it updates running_bw).
 */
static void task_non_contending(struct task_struct *p)
{
        struct sched_dl_entity *dl_se = &p->dl;
        struct hrtimer *timer = &dl_se->inactive_timer;
        struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
        struct rq *rq = rq_of_dl_rq(dl_rq);
        s64 zerolag_time;

        /*
         * If this is a non-deadline task that has been boosted,
         * do nothing
         */
        if (dl_se->dl_runtime == 0)
                return;

        if (dl_entity_is_special(dl_se))
                return;

        WARN_ON(dl_se->dl_non_contending);

        zerolag_time = dl_se->deadline -
                 div64_long((dl_se->runtime * dl_se->dl_period),
                        dl_se->dl_runtime);

        /*
         * Using relative times instead of the absolute "0-lag time"
         * allows to simplify the code
         */
        zerolag_time -= rq_clock(rq);

        /*
         * If the "0-lag time" already passed, decrease the active
         * utilization now, instead of starting a timer
         */
        if ((zerolag_time < 0) || hrtimer_active(&dl_se->inactive_timer)) {
                if (dl_task(p))
                        sub_running_bw(dl_se, dl_rq);
                if (!dl_task(p) || READ_ONCE(p->__state) == TASK_DEAD) {
                        struct dl_bw *dl_b = dl_bw_of(task_cpu(p));

                        if (READ_ONCE(p->__state) == TASK_DEAD)
                                sub_rq_bw(&p->dl, &rq->dl);
                        raw_spin_lock(&dl_b->lock);
                        __dl_sub(dl_b, p->dl.dl_bw, dl_bw_cpus(task_cpu(p)));
                        __dl_clear_params(p);
                        raw_spin_unlock(&dl_b->lock);
                }

                return;
        }

        dl_se->dl_non_contending = 1;
        get_task_struct(p);
        hrtimer_start(timer, ns_to_ktime(zerolag_time), HRTIMER_MODE_REL_HARD);
}

static void task_contending(struct sched_dl_entity *dl_se, int flags)
{
        struct dl_rq *dl_rq = dl_rq_of_se(dl_se);

        /*
         * If this is a non-deadline task that has been boosted,
         * do nothing
         */
        if (dl_se->dl_runtime == 0)
                return;

        if (flags & ENQUEUE_MIGRATED)
                add_rq_bw(dl_se, dl_rq);

        if (dl_se->dl_non_contending) {
                dl_se->dl_non_contending = 0;
                /*
                 * If the timer handler is currently running and the
                 * timer cannot be canceled, inactive_task_timer()
                 * will see that dl_not_contending is not set, and
                 * will not touch the rq's active utilization,
                 * so we are still safe.
                 */
                if (hrtimer_try_to_cancel(&dl_se->inactive_timer) == 1)
                        put_task_struct(dl_task_of(dl_se));
        } else {
                /*
                 * Since "dl_non_contending" is not set, the
                 * task's utilization has already been removed from
                 * active utilization (either when the task blocked,
                 * when the "inactive timer" fired).
                 * So, add it back.
                 */
                add_running_bw(dl_se, dl_rq);
        }
}

static inline int is_leftmost(struct task_struct *p, struct dl_rq *dl_rq)
{
        struct sched_dl_entity *dl_se = &p->dl;

        return dl_rq->root.rb_leftmost == &dl_se->rb_node;
}

static void init_dl_rq_bw_ratio(struct dl_rq *dl_rq);

void init_dl_bandwidth(struct dl_bandwidth *dl_b, u64 period, u64 runtime)
{
        raw_spin_lock_init(&dl_b->dl_runtime_lock);
        dl_b->dl_period = period;
        dl_b->dl_runtime = runtime;
}

void init_dl_bw(struct dl_bw *dl_b)
{
        raw_spin_lock_init(&dl_b->lock);
        raw_spin_lock(&def_dl_bandwidth.dl_runtime_lock);
        if (global_rt_runtime() == RUNTIME_INF)
                dl_b->bw = -1;
        else
                dl_b->bw = to_ratio(global_rt_period(), global_rt_runtime());
        raw_spin_unlock(&def_dl_bandwidth.dl_runtime_lock);
        dl_b->total_bw = 0;
}

void init_dl_rq(struct dl_rq *dl_rq)
{
        dl_rq->root = RB_ROOT_CACHED;

#ifdef CONFIG_SMP
        /* zero means no -deadline tasks */
        dl_rq->earliest_dl.curr = dl_rq->earliest_dl.next = 0;

        dl_rq->dl_nr_migratory = 0;
        dl_rq->overloaded = 0;
        dl_rq->pushable_dl_tasks_root = RB_ROOT_CACHED;
#else
        init_dl_bw(&dl_rq->dl_bw);
#endif

        dl_rq->running_bw = 0;
        dl_rq->this_bw = 0;
        init_dl_rq_bw_ratio(dl_rq);
}

#ifdef CONFIG_SMP

static inline int dl_overloaded(struct rq *rq)
{
        return atomic_read(&rq->rd->dlo_count);
}

static inline void dl_set_overload(struct rq *rq)
{
        if (!rq->online)
                return;

        cpumask_set_cpu(rq->cpu, rq->rd->dlo_mask);
        /*
         * Must be visible before the overload count is
         * set (as in sched_rt.c).
         *
         * Matched by the barrier in pull_dl_task().
         */
        smp_wmb();
        atomic_inc(&rq->rd->dlo_count);
}

static inline void dl_clear_overload(struct rq *rq)
{
        if (!rq->online)
                return;

        atomic_dec(&rq->rd->dlo_count);
        cpumask_clear_cpu(rq->cpu, rq->rd->dlo_mask);
}

static void update_dl_migration(struct dl_rq *dl_rq)
{
        if (dl_rq->dl_nr_migratory && dl_rq->dl_nr_running > 1) {
                if (!dl_rq->overloaded) {
                        dl_set_overload(rq_of_dl_rq(dl_rq));
                        dl_rq->overloaded = 1;
                }
        } else if (dl_rq->overloaded) {
                dl_clear_overload(rq_of_dl_rq(dl_rq));
                dl_rq->overloaded = 0;
        }
}

static void inc_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
        struct task_struct *p = dl_task_of(dl_se);

        if (p->nr_cpus_allowed > 1)
                dl_rq->dl_nr_migratory++;

        update_dl_migration(dl_rq);
}

static void dec_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
        struct task_struct *p = dl_task_of(dl_se);

        if (p->nr_cpus_allowed > 1)
                dl_rq->dl_nr_migratory--;

        update_dl_migration(dl_rq);
}

#define __node_2_pdl(node) \
        rb_entry((node), struct task_struct, pushable_dl_tasks)

static inline bool __pushable_less(struct rb_node *a, const struct rb_node *b)
{
        return dl_entity_preempt(&__node_2_pdl(a)->dl, &__node_2_pdl(b)->dl);
}

/*
 * The list of pushable -deadline task is not a plist, like in
 * sched_rt.c, it is an rb-tree with tasks ordered by deadline.
 */
static void enqueue_pushable_dl_task(struct rq *rq, struct task_struct *p)
{
        struct rb_node *leftmost;

        BUG_ON(!RB_EMPTY_NODE(&p->pushable_dl_tasks));

        leftmost = rb_add_cached(&p->pushable_dl_tasks,
                                 &rq->dl.pushable_dl_tasks_root,
                                 __pushable_less);
        if (leftmost)
                rq->dl.earliest_dl.next = p->dl.deadline;
}

static void dequeue_pushable_dl_task(struct rq *rq, struct task_struct *p)
{
        struct dl_rq *dl_rq = &rq->dl;
        struct rb_root_cached *root = &dl_rq->pushable_dl_tasks_root;
        struct rb_node *leftmost;

        if (RB_EMPTY_NODE(&p->pushable_dl_tasks))
                return;

        leftmost = rb_erase_cached(&p->pushable_dl_tasks, root);
        if (leftmost)
                dl_rq->earliest_dl.next = __node_2_pdl(leftmost)->dl.deadline;

        RB_CLEAR_NODE(&p->pushable_dl_tasks);
}

static inline int has_pushable_dl_tasks(struct rq *rq)
{
        return !RB_EMPTY_ROOT(&rq->dl.pushable_dl_tasks_root.rb_root);
}

static int push_dl_task(struct rq *rq);

static inline bool need_pull_dl_task(struct rq *rq, struct task_struct *prev)
{
        return rq->online && dl_task(prev);
}

static DEFINE_PER_CPU(struct callback_head, dl_push_head);
static DEFINE_PER_CPU(struct callback_head, dl_pull_head);

static void push_dl_tasks(struct rq *);
static void pull_dl_task(struct rq *);

static inline void deadline_queue_push_tasks(struct rq *rq)
{
        if (!has_pushable_dl_tasks(rq))
                return;

        queue_balance_callback(rq, &per_cpu(dl_push_head, rq->cpu), push_dl_tasks);
}

static inline void deadline_queue_pull_task(struct rq *rq)
{
        queue_balance_callback(rq, &per_cpu(dl_pull_head, rq->cpu), pull_dl_task);
}

static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq);

static struct rq *dl_task_offline_migration(struct rq *rq, struct task_struct *p)
{
        struct rq *later_rq = NULL;
        struct dl_bw *dl_b;

        later_rq = find_lock_later_rq(p, rq);
        if (!later_rq) {
                int cpu;

                /*
                 * If we cannot preempt any rq, fall back to pick any
                 * online CPU:
                 */
                cpu = cpumask_any_and(cpu_active_mask, p->cpus_ptr);
                if (cpu >= nr_cpu_ids) {
                        /*
                         * Failed to find any suitable CPU.
                         * The task will never come back!
                         */
                        BUG_ON(dl_bandwidth_enabled());

                        /*
                         * If admission control is disabled we
                         * try a little harder to let the task
                         * run.
                         */
                        cpu = cpumask_any(cpu_active_mask);
                }
                later_rq = cpu_rq(cpu);
                double_lock_balance(rq, later_rq);
        }

        if (p->dl.dl_non_contending || p->dl.dl_throttled) {
                /*
                 * Inactive timer is armed (or callback is running, but
                 * waiting for us to release rq locks). In any case, when it
                 * will fire (or continue), it will see running_bw of this
                 * task migrated to later_rq (and correctly handle it).
                 */
                sub_running_bw(&p->dl, &rq->dl);
                sub_rq_bw(&p->dl, &rq->dl);

                add_rq_bw(&p->dl, &later_rq->dl);
                add_running_bw(&p->dl, &later_rq->dl);
        } else {
                sub_rq_bw(&p->dl, &rq->dl);
                add_rq_bw(&p->dl, &later_rq->dl);
        }

        /*
         * And we finally need to fixup root_domain(s) bandwidth accounting,
         * since p is still hanging out in the old (now moved to default) root
         * domain.
         */
        dl_b = &rq->rd->dl_bw;
        raw_spin_lock(&dl_b->lock);
        __dl_sub(dl_b, p->dl.dl_bw, cpumask_weight(rq->rd->span));
        raw_spin_unlock(&dl_b->lock);

        dl_b = &later_rq->rd->dl_bw;
        raw_spin_lock(&dl_b->lock);
        __dl_add(dl_b, p->dl.dl_bw, cpumask_weight(later_rq->rd->span));
        raw_spin_unlock(&dl_b->lock);

        set_task_cpu(p, later_rq->cpu);
        double_unlock_balance(later_rq, rq);

        return later_rq;
}

#else

static inline
void enqueue_pushable_dl_task(struct rq *rq, struct task_struct *p)
{
}

static inline
void dequeue_pushable_dl_task(struct rq *rq, struct task_struct *p)
{
}

static inline
void inc_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
}

static inline
void dec_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
}

static inline bool need_pull_dl_task(struct rq *rq, struct task_struct *prev)
{
        return false;
}

static inline void pull_dl_task(struct rq *rq)
{
}

static inline void deadline_queue_push_tasks(struct rq *rq)
{
}

static inline void deadline_queue_pull_task(struct rq *rq)
{
}
#endif /* CONFIG_SMP */

static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags);
static void __dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags);
static void check_preempt_curr_dl(struct rq *rq, struct task_struct *p, int flags);

/*
 * We are being explicitly informed that a new instance is starting,
 * and this means that:
 *  - the absolute deadline of the entity has to be placed at
 *    current time + relative deadline;
 *  - the runtime of the entity has to be set to the maximum value.
 *
 * The capability of specifying such event is useful whenever a -deadline
 * entity wants to (try to!) synchronize its behaviour with the scheduler's
 * one, and to (try to!) reconcile itself with its own scheduling
 * parameters.
 */
static inline void setup_new_dl_entity(struct sched_dl_entity *dl_se)
{
        struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
        struct rq *rq = rq_of_dl_rq(dl_rq);

        WARN_ON(is_dl_boosted(dl_se));
        WARN_ON(dl_time_before(rq_clock(rq), dl_se->deadline));

        /*
         * We are racing with the deadline timer. So, do nothing because
         * the deadline timer handler will take care of properly recharging
         * the runtime and postponing the deadline
         */
        if (dl_se->dl_throttled)
                return;

        /*
         * We use the regular wall clock time to set deadlines in the
         * future; in fact, we must consider execution overheads (time
         * spent on hardirq context, etc.).
         */
        dl_se->deadline = rq_clock(rq) + dl_se->dl_deadline;
        dl_se->runtime = dl_se->dl_runtime;
}

/*
 * Pure Earliest Deadline First (EDF) scheduling does not deal with the
 * possibility of a entity lasting more than what it declared, and thus
 * exhausting its runtime.
 *
 * Here we are interested in making runtime overrun possible, but we do
 * not want a entity which is misbehaving to affect the scheduling of all
 * other entities.
 * Therefore, a budgeting strategy called Constant Bandwidth Server (CBS)
 * is used, in order to confine each entity within its own bandwidth.
 *
 * This function deals exactly with that, and ensures that when the runtime
 * of a entity is replenished, its deadline is also postponed. That ensures
 * the overrunning entity can't interfere with other entity in the system and
 * can't make them miss their deadlines. Reasons why this kind of overruns
 * could happen are, typically, a entity voluntarily trying to overcome its
 * runtime, or it just underestimated it during sched_setattr().
 */
static void replenish_dl_entity(struct sched_dl_entity *dl_se)
{
        struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
        struct rq *rq = rq_of_dl_rq(dl_rq);

        BUG_ON(pi_of(dl_se)->dl_runtime <= 0);

        /*
         * This could be the case for a !-dl task that is boosted.
         * Just go with full inherited parameters.
         */
        if (dl_se->dl_deadline == 0) {
                dl_se->deadline = rq_clock(rq) + pi_of(dl_se)->dl_deadline;
                dl_se->runtime = pi_of(dl_se)->dl_runtime;
        }

        if (dl_se->dl_yielded && dl_se->runtime > 0)
                dl_se->runtime = 0;

        /*
         * We keep moving the deadline away until we get some
         * available runtime for the entity. This ensures correct
         * handling of situations where the runtime overrun is
         * arbitrary large.
         */
        while (dl_se->runtime <= 0) {
                dl_se->deadline += pi_of(dl_se)->dl_period;
                dl_se->runtime += pi_of(dl_se)->dl_runtime;
        }

        /*
         * At this point, the deadline really should be "in
         * the future" with respect to rq->clock. If it's
         * not, we are, for some reason, lagging too much!
         * Anyway, after having warn userspace abut that,
         * we still try to keep the things running by
         * resetting the deadline and the budget of the
         * entity.
         */
        if (dl_time_before(dl_se->deadline, rq_clock(rq))) {
                printk_deferred_once("sched: DL replenish lagged too much\n");
                dl_se->deadline = rq_clock(rq) + pi_of(dl_se)->dl_deadline;
                dl_se->runtime = pi_of(dl_se)->dl_runtime;
        }

        if (dl_se->dl_yielded)
                dl_se->dl_yielded = 0;
        if (dl_se->dl_throttled)
                dl_se->dl_throttled = 0;
}

/*
 * Here we check if --at time t-- an entity (which is probably being
 * [re]activated or, in general, enqueued) can use its remaining runtime
 * and its current deadline _without_ exceeding the bandwidth it is
 * assigned (function returns true if it can't). We are in fact applying
 * one of the CBS rules: when a task wakes up, if the residual runtime
 * over residual deadline fits within the allocated bandwidth, then we
 * can keep the current (absolute) deadline and residual budget without
 * disrupting the schedulability of the system. Otherwise, we should
 * refill the runtime and set the deadline a period in the future,
 * because keeping the current (absolute) deadline of the task would
 * result in breaking guarantees promised to other tasks (refer to
 * Documentation/scheduler/sched-deadline.rst for more information).
 *
 * This function returns true if:
 *
 *   runtime / (deadline - t) > dl_runtime / dl_deadline ,
 *
 * IOW we can't recycle current parameters.
 *
 * Notice that the bandwidth check is done against the deadline. For
 * task with deadline equal to period this is the same of using
 * dl_period instead of dl_deadline in the equation above.
 */
static bool dl_entity_overflow(struct sched_dl_entity *dl_se, u64 t)
{
        u64 left, right;

        /*
         * left and right are the two sides of the equation above,
         * after a bit of shuffling to use multiplications instead
         * of divisions.
         *
         * Note that none of the time values involved in the two
         * multiplications are absolute: dl_deadline and dl_runtime
         * are the relative deadline and the maximum runtime of each
         * instance, runtime is the runtime left for the last instance
         * and (deadline - t), since t is rq->clock, is the time left
         * to the (absolute) deadline. Even if overflowing the u64 type
         * is very unlikely to occur in both cases, here we scale down
         * as we want to avoid that risk at all. Scaling down by 10
         * means that we reduce granularity to 1us. We are fine with it,
         * since this is only a true/false check and, anyway, thinking
         * of anything below microseconds resolution is actually fiction
         * (but still we want to give the user that illusion >;).
         */
        left = (pi_of(dl_se)->dl_deadline >> DL_SCALE) * (dl_se->runtime >> DL_SCALE);
        right = ((dl_se->deadline - t) >> DL_SCALE) *
                (pi_of(dl_se)->dl_runtime >> DL_SCALE);

        return dl_time_before(right, left);
}

/*
 * Revised wakeup rule [1]: For self-suspending tasks, rather then
 * re-initializing task's runtime and deadline, the revised wakeup
 * rule adjusts the task's runtime to avoid the task to overrun its
 * density.
 *
 * Reasoning: a task may overrun the density if:
 *    runtime / (deadline - t) > dl_runtime / dl_deadline
 *
 * Therefore, runtime can be adjusted to:
 *     runtime = (dl_runtime / dl_deadline) * (deadline - t)
 *
 * In such way that runtime will be equal to the maximum density
 * the task can use without breaking any rule.
 *
 * [1] Luca Abeni, Giuseppe Lipari, and Juri Lelli. 2015. Constant
 * bandwidth server revisited. SIGBED Rev. 11, 4 (January 2015), 19-24.
 */
static void
update_dl_revised_wakeup(struct sched_dl_entity *dl_se, struct rq *rq)
{
        u64 laxity = dl_se->deadline - rq_clock(rq);

        /*
         * If the task has deadline < period, and the deadline is in the past,
         * it should already be throttled before this check.
         *
         * See update_dl_entity() comments for further details.
         */
        WARN_ON(dl_time_before(dl_se->deadline, rq_clock(rq)));

        dl_se->runtime = (dl_se->dl_density * laxity) >> BW_SHIFT;
}

/*
 * Regarding the deadline, a task with implicit deadline has a relative
 * deadline == relative period. A task with constrained deadline has a
 * relative deadline <= relative period.
 *
 * We support constrained deadline tasks. However, there are some restrictions
 * applied only for tasks which do not have an implicit deadline. See
 * update_dl_entity() to know more about such restrictions.
 *
 * The dl_is_implicit() returns true if the task has an implicit deadline.
 */
static inline bool dl_is_implicit(struct sched_dl_entity *dl_se)
{
        return dl_se->dl_deadline == dl_se->dl_period;
}

/*
 * When a deadline entity is placed in the runqueue, its runtime and deadline
 * might need to be updated. This is done by a CBS wake up rule. There are two
 * different rules: 1) the original CBS; and 2) the Revisited CBS.
 *
 * When the task is starting a new period, the Original CBS is used. In this
 * case, the runtime is replenished and a new absolute deadline is set.
 *
 * When a task is queued before the begin of the next period, using the
 * remaining runtime and deadline could make the entity to overflow, see
 * dl_entity_overflow() to find more about runtime overflow. When such case
 * is detected, the runtime and deadline need to be updated.
 *
 * If the task has an implicit deadline, i.e., deadline == period, the Original
 * CBS is applied. the runtime is replenished and a new absolute deadline is
 * set, as in the previous cases.
 *
 * However, the Original CBS does not work properly for tasks with
 * deadline < period, which are said to have a constrained deadline. By
 * applying the Original CBS, a constrained deadline task would be able to run
 * runtime/deadline in a period. With deadline < period, the task would
 * overrun the runtime/period allowed bandwidth, breaking the admission test.
 *
 * In order to prevent this misbehave, the Revisited CBS is used for
 * constrained deadline tasks when a runtime overflow is detected. In the
 * Revisited CBS, rather than replenishing & setting a new absolute deadline,
 * the remaining runtime of the task is reduced to avoid runtime overflow.
 * Please refer to the comments update_dl_revised_wakeup() function to find
 * more about the Revised CBS rule.
 */
static void update_dl_entity(struct sched_dl_entity *dl_se)
{
        struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
        struct rq *rq = rq_of_dl_rq(dl_rq);

        if (dl_time_before(dl_se->deadline, rq_clock(rq)) ||
            dl_entity_overflow(dl_se, rq_clock(rq))) {

                if (unlikely(!dl_is_implicit(dl_se) &&
                             !dl_time_before(dl_se->deadline, rq_clock(rq)) &&
                             !is_dl_boosted(dl_se))) {
                        update_dl_revised_wakeup(dl_se, rq);
                        return;
                }

                dl_se->deadline = rq_clock(rq) + pi_of(dl_se)->dl_deadline;
                dl_se->runtime = pi_of(dl_se)->dl_runtime;
        }
}

static inline u64 dl_next_period(struct sched_dl_entity *dl_se)
{
        return dl_se->deadline - dl_se->dl_deadline + dl_se->dl_period;
}

/*
 * If the entity depleted all its runtime, and if we want it to sleep
 * while waiting for some new execution time to become available, we
 * set the bandwidth replenishment timer to the replenishment instant
 * and try to activate it.
 *
 * Notice that it is important for the caller to know if the timer
 * actually started or not (i.e., the replenishment instant is in
 * the future or in the past).
 */
static int start_dl_timer(struct task_struct *p)
{
        struct sched_dl_entity *dl_se = &p->dl;
        struct hrtimer *timer = &dl_se->dl_timer;
        struct rq *rq = task_rq(p);
        ktime_t now, act;
        s64 delta;

        lockdep_assert_rq_held(rq);

        /*
         * We want the timer to fire at the deadline, but considering
         * that it is actually coming from rq->clock and not from
         * hrtimer's time base reading.
         */
        act = ns_to_ktime(dl_next_period(dl_se));
        now = hrtimer_cb_get_time(timer);
        delta = ktime_to_ns(now) - rq_clock(rq);
        act = ktime_add_ns(act, delta);

        /*
         * If the expiry time already passed, e.g., because the value
         * chosen as the deadline is too small, don't even try to
         * start the timer in the past!
         */
        if (ktime_us_delta(act, now) < 0)
                return 0;

        /*
         * !enqueued will guarantee another callback; even if one is already in
         * progress. This ensures a balanced {get,put}_task_struct().
         *
         * The race against __run_timer() clearing the enqueued state is
         * harmless because we're holding task_rq()->lock, therefore the timer
         * expiring after we've done the check will wait on its task_rq_lock()
         * and observe our state.
         */
        if (!hrtimer_is_queued(timer)) {
                get_task_struct(p);
                hrtimer_start(timer, act, HRTIMER_MODE_ABS_HARD);
        }

        return 1;
}

/*
 * This is the bandwidth enforcement timer callback. If here, we know
 * a task is not on its dl_rq, since the fact that the timer was running
 * means the task is throttled and needs a runtime replenishment.
 *
 * However, what we actually do depends on the fact the task is active,
 * (it is on its rq) or has been removed from there by a call to
 * dequeue_task_dl(). In the former case we must issue the runtime
 * replenishment and add the task back to the dl_rq; in the latter, we just
 * do nothing but clearing dl_throttled, so that runtime and deadline
 * updating (and the queueing back to dl_rq) will be done by the
 * next call to enqueue_task_dl().
 */
static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
{
        struct sched_dl_entity *dl_se = container_of(timer,
                                                     struct sched_dl_entity,
                                                     dl_timer);
        struct task_struct *p = dl_task_of(dl_se);
        struct rq_flags rf;
        struct rq *rq;

        rq = task_rq_lock(p, &rf);

        /*
         * The task might have changed its scheduling policy to something
         * different than SCHED_DEADLINE (through switched_from_dl()).
         */
        if (!dl_task(p))
                goto unlock;

        /*
         * The task might have been boosted by someone else and might be in the
         * boosting/deboosting path, its not throttled.
         */
        if (is_dl_boosted(dl_se))
                goto unlock;

        /*
         * Spurious timer due to start_dl_timer() race; or we already received
         * a replenishment from rt_mutex_setprio().
         */
        if (!dl_se->dl_throttled)
                goto unlock;

        sched_clock_tick();
        update_rq_clock(rq);

        /*
         * If the throttle happened during sched-out; like:
         *
         *   schedule()
         *     deactivate_task()
         *       dequeue_task_dl()
         *         update_curr_dl()
         *           start_dl_timer()
         *         __dequeue_task_dl()
         *     prev->on_rq = 0;
         *
         * We can be both throttled and !queued. Replenish the counter
         * but do not enqueue -- wait for our wakeup to do that.
         */
        if (!task_on_rq_queued(p)) {
                replenish_dl_entity(dl_se);
                goto unlock;
        }

#ifdef CONFIG_SMP
        if (unlikely(!rq->online)) {
                /*
                 * If the runqueue is no longer available, migrate the
                 * task elsewhere. This necessarily changes rq.
                 */
                lockdep_unpin_lock(__rq_lockp(rq), rf.cookie);
                rq = dl_task_offline_migration(rq, p);
                rf.cookie = lockdep_pin_lock(__rq_lockp(rq));
                update_rq_clock(rq);

                /*
                 * Now that the task has been migrated to the new RQ and we
                 * have that locked, proceed as normal and enqueue the task
                 * there.
                 */
        }
#endif

        enqueue_task_dl(rq, p, ENQUEUE_REPLENISH);
        if (dl_task(rq->curr))
                check_preempt_curr_dl(rq, p, 0);
        else
                resched_curr(rq);

#ifdef CONFIG_SMP
        /*
         * Queueing this task back might have overloaded rq, check if we need
         * to kick someone away.
         */
        if (has_pushable_dl_tasks(rq)) {
                /*
                 * Nothing relies on rq->lock after this, so its safe to drop
                 * rq->lock.
                 */
                rq_unpin_lock(rq, &rf);
                push_dl_task(rq);
                rq_repin_lock(rq, &rf);
        }
#endif

unlock:
        task_rq_unlock(rq, p, &rf);

        /*
         * This can free the task_struct, including this hrtimer, do not touch
         * anything related to that after this.
         */
        put_task_struct(p);

        return HRTIMER_NORESTART;
}

void init_dl_task_timer(struct sched_dl_entity *dl_se)
{
        struct hrtimer *timer = &dl_se->dl_timer;

        hrtimer_init(timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
        timer->function = dl_task_timer;
}

/*
 * During the activation, CBS checks if it can reuse the current task's
 * runtime and period. If the deadline of the task is in the past, CBS
 * cannot use the runtime, and so it replenishes the task. This rule
 * works fine for implicit deadline tasks (deadline == period), and the
 * CBS was designed for implicit deadline tasks. However, a task with
 * constrained deadline (deadline < period) might be awakened after the
 * deadline, but before the next period. In this case, replenishing the
 * task would allow it to run for runtime / deadline. As in this case
 * deadline < period, CBS enables a task to run for more than the
 * runtime / period. In a very loaded system, this can cause a domino
 * effect, making other tasks miss their deadlines.
 *
 * To avoid this problem, in the activation of a constrained deadline
 * task after the deadline but before the next period, throttle the
 * task and set the replenishing timer to the begin of the next period,
 * unless it is boosted.
 */
static inline void dl_check_constrained_dl(struct sched_dl_entity *dl_se)
{
        struct task_struct *p = dl_task_of(dl_se);
        struct rq *rq = rq_of_dl_rq(dl_rq_of_se(dl_se));

        if (dl_time_before(dl_se->deadline, rq_clock(rq)) &&
            dl_time_before(rq_clock(rq), dl_next_period(dl_se))) {
                if (unlikely(is_dl_boosted(dl_se) || !start_dl_timer(p)))
                        return;
                dl_se->dl_throttled = 1;
                if (dl_se->runtime > 0)
                        dl_se->runtime = 0;
        }
}

static
int dl_runtime_exceeded(struct sched_dl_entity *dl_se)
{
        return (dl_se->runtime <= 0);
}

extern bool sched_rt_bandwidth_account(struct rt_rq *rt_rq);

/*
 * This function implements the GRUB accounting rule:
 * according to the GRUB reclaiming algorithm, the runtime is
 * not decreased as "dq = -dt", but as
 * "dq = -max{u / Umax, (1 - Uinact - Uextra)} dt",
 * where u is the utilization of the task, Umax is the maximum reclaimable
 * utilization, Uinact is the (per-runqueue) inactive utilization, computed
 * as the difference between the "total runqueue utilization" and the
 * runqueue active utilization, and Uextra is the (per runqueue) extra
 * reclaimable utilization.
 * Since rq->dl.running_bw and rq->dl.this_bw contain utilizations
 * multiplied by 2^BW_SHIFT, the result has to be shifted right by
 * BW_SHIFT.
 * Since rq->dl.bw_ratio contains 1 / Umax multiplied by 2^RATIO_SHIFT,
 * dl_bw is multiped by rq->dl.bw_ratio and shifted right by RATIO_SHIFT.
 * Since delta is a 64 bit variable, to have an overflow its value
 * should be larger than 2^(64 - 20 - 8), which is more than 64 seconds.
 * So, overflow is not an issue here.
 */
static u64 grub_reclaim(u64 delta, struct rq *rq, struct sched_dl_entity *dl_se)
{
        u64 u_inact = rq->dl.this_bw - rq->dl.running_bw; /* Utot - Uact */
        u64 u_act;
        u64 u_act_min = (dl_se->dl_bw * rq->dl.bw_ratio) >> RATIO_SHIFT;

        /*
         * Instead of computing max{u * bw_ratio, (1 - u_inact - u_extra)},
         * we compare u_inact + rq->dl.extra_bw with
         * 1 - (u * rq->dl.bw_ratio >> RATIO_SHIFT), because
         * u_inact + rq->dl.extra_bw can be larger than
         * 1 * (so, 1 - u_inact - rq->dl.extra_bw would be negative
         * leading to wrong results)
         */
        if (u_inact + rq->dl.extra_bw > BW_UNIT - u_act_min)
                u_act = u_act_min;
        else
                u_act = BW_UNIT - u_inact - rq->dl.extra_bw;

        return (delta * u_act) >> BW_SHIFT;
}

/*
 * Update the current task's runtime statistics (provided it is still
 * a -deadline task and has not been removed from the dl_rq).
 */
static void update_curr_dl(struct rq *rq)
{
        struct task_struct *curr = rq->curr;
        struct sched_dl_entity *dl_se = &curr->dl;
        u64 delta_exec, scaled_delta_exec;
        int cpu = cpu_of(rq);
        u64 now;

        if (!dl_task(curr) || !on_dl_rq(dl_se))
                return;

        /*
         * Consumed budget is computed considering the time as
         * observed by schedulable tasks (excluding time spent
         * in hardirq context, etc.). Deadlines are instead
         * computed using hard walltime. This seems to be the more
         * natural solution, but the full ramifications of this
         * approach need further study.
         */
        now = rq_clock_task(rq);
        delta_exec = now - curr->se.exec_start;
        if (unlikely((s64)delta_exec <= 0)) {
                if (unlikely(dl_se->dl_yielded))
                        goto throttle;
                return;
        }

        schedstat_set(curr->se.statistics.exec_max,
                      max(curr->se.statistics.exec_max, delta_exec));

        curr->se.sum_exec_runtime += delta_exec;
        account_group_exec_runtime(curr, delta_exec);

        curr->se.exec_start = now;
        cgroup_account_cputime(curr, delta_exec);

        if (dl_entity_is_special(dl_se))
                return;

        /*
         * For tasks that participate in GRUB, we implement GRUB-PA: the
         * spare reclaimed bandwidth is used to clock down frequency.
         *
         * For the others, we still need to scale reservation parameters
         * according to current frequency and CPU maximum capacity.
         */
        if (unlikely(dl_se->flags & SCHED_FLAG_RECLAIM)) {
                scaled_delta_exec = grub_reclaim(delta_exec,
                                                 rq,
                                                 &curr->dl);
        } else {
                unsigned long scale_freq = arch_scale_freq_capacity(cpu);
                unsigned long scale_cpu = arch_scale_cpu_capacity(cpu);

                scaled_delta_exec = cap_scale(delta_exec, scale_freq);
                scaled_delta_exec = cap_scale(scaled_delta_exec, scale_cpu);
        }

        dl_se->runtime -= scaled_delta_exec;

throttle:
        if (dl_runtime_exceeded(dl_se) || dl_se->dl_yielded) {
                dl_se->dl_throttled = 1;

                /* If requested, inform the user about runtime overruns. */
                if (dl_runtime_exceeded(dl_se) &&
                    (dl_se->flags & SCHED_FLAG_DL_OVERRUN))
                        dl_se->dl_overrun = 1;

                __dequeue_task_dl(rq, curr, 0);
                if (unlikely(is_dl_boosted(dl_se) || !start_dl_timer(curr)))
                        enqueue_task_dl(rq, curr, ENQUEUE_REPLENISH);

                if (!is_leftmost(curr, &rq->dl))
                        resched_curr(rq);
        }

        /*
         * Because -- for now -- we share the rt bandwidth, we need to
         * account our runtime there too, otherwise actual rt tasks
         * would be able to exceed the shared quota.
         *
         * Account to the root rt group for now.
         *
         * The solution we're working towards is having the RT groups scheduled
         * using deadline servers -- however there's a few nasties to figure
         * out before that can happen.
         */
        if (rt_bandwidth_enabled()) {
                struct rt_rq *rt_rq = &rq->rt;

                raw_spin_lock(&rt_rq->rt_runtime_lock);
                /*
                 * We'll let actual RT tasks worry about the overflow here, we
                 * have our own CBS to keep us inline; only account when RT
                 * bandwidth is relevant.
                 */
                if (sched_rt_bandwidth_account(rt_rq))
                        rt_rq->rt_time += delta_exec;
                raw_spin_unlock(&rt_rq->rt_runtime_lock);
        }
}

static enum hrtimer_restart inactive_task_timer(struct hrtimer *timer)
{
        struct sched_dl_entity *dl_se = container_of(timer,
                                                     struct sched_dl_entity,
                                                     inactive_timer);
        struct task_struct *p = dl_task_of(dl_se);
        struct rq_flags rf;
        struct rq *rq;

        rq = task_rq_lock(p, &rf);

        sched_clock_tick();
        update_rq_clock(rq);

        if (!dl_task(p) || READ_ONCE(p->__state) == TASK_DEAD) {
                struct dl_bw *dl_b = dl_bw_of(task_cpu(p));

                if (READ_ONCE(p->__state) == TASK_DEAD && dl_se->dl_non_contending) {
                        sub_running_bw(&p->dl, dl_rq_of_se(&p->dl));
                        sub_rq_bw(&p->dl, dl_rq_of_se(&p->dl));
                        dl_se->dl_non_contending = 0;
                }

                raw_spin_lock(&dl_b->lock);
                __dl_sub(dl_b, p->dl.dl_bw, dl_bw_cpus(task_cpu(p)));
                raw_spin_unlock(&dl_b->lock);
                __dl_clear_params(p);

                goto unlock;
        }
        if (dl_se->dl_non_contending == 0)
                goto unlock;

        sub_running_bw(dl_se, &rq->dl);
        dl_se->dl_non_contending = 0;
unlock:
        task_rq_unlock(rq, p, &rf);
        put_task_struct(p);

        return HRTIMER_NORESTART;
}

void init_dl_inactive_task_timer(struct sched_dl_entity *dl_se)
{
        struct hrtimer *timer = &dl_se->inactive_timer;

        hrtimer_init(timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
        timer->function = inactive_task_timer;
}

#ifdef CONFIG_SMP

static void inc_dl_deadline(struct dl_rq *dl_rq, u64 deadline)
{
        struct rq *rq = rq_of_dl_rq(dl_rq);

        if (dl_rq->earliest_dl.curr == 0 ||
            dl_time_before(deadline, dl_rq->earliest_dl.curr)) {
                if (dl_rq->earliest_dl.curr == 0)
                        cpupri_set(&rq->rd->cpupri, rq->cpu, CPUPRI_HIGHER);
                dl_rq->earliest_dl.curr = deadline;
                cpudl_set(&rq->rd->cpudl, rq->cpu, deadline);
        }
}

static void dec_dl_deadline(struct dl_rq *dl_rq, u64 deadline)
{
        struct rq *rq = rq_of_dl_rq(dl_rq);

        /*
         * Since we may have removed our earliest (and/or next earliest)
         * task we must recompute them.
         */
        if (!dl_rq->dl_nr_running) {
                dl_rq->earliest_dl.curr = 0;
                dl_rq->earliest_dl.next = 0;
                cpudl_clear(&rq->rd->cpudl, rq->cpu);
                cpupri_set(&rq->rd->cpupri, rq->cpu, rq->rt.highest_prio.curr);
        } else {
                struct rb_node *leftmost = dl_rq->root.rb_leftmost;
                struct sched_dl_entity *entry;

                entry = rb_entry(leftmost, struct sched_dl_entity, rb_node);
                dl_rq->earliest_dl.curr = entry->deadline;
                cpudl_set(&rq->rd->cpudl, rq->cpu, entry->deadline);
        }
}

#else

static inline void inc_dl_deadline(struct dl_rq *dl_rq, u64 deadline) {}
static inline void dec_dl_deadline(struct dl_rq *dl_rq, u64 deadline) {}

#endif /* CONFIG_SMP */

static inline
void inc_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
        int prio = dl_task_of(dl_se)->prio;
        u64 deadline = dl_se->deadline;

        WARN_ON(!dl_prio(prio));
        dl_rq->dl_nr_running++;
        add_nr_running(rq_of_dl_rq(dl_rq), 1);

        inc_dl_deadline(dl_rq, deadline);
        inc_dl_migration(dl_se, dl_rq);
}

static inline
void dec_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
        int prio = dl_task_of(dl_se)->prio;

        WARN_ON(!dl_prio(prio));
        WARN_ON(!dl_rq->dl_nr_running);
        dl_rq->dl_nr_running--;
        sub_nr_running(rq_of_dl_rq(dl_rq), 1);

        dec_dl_deadline(dl_rq, dl_se->deadline);
        dec_dl_migration(dl_se, dl_rq);
}

#define __node_2_dle(node) \
        rb_entry((node), struct sched_dl_entity, rb_node)

static inline bool __dl_less(struct rb_node *a, const struct rb_node *b)
{
        return dl_time_before(__node_2_dle(a)->deadline, __node_2_dle(b)->deadline);
}

static void __enqueue_dl_entity(struct sched_dl_entity *dl_se)
{
        struct dl_rq *dl_rq = dl_rq_of_se(dl_se);

        BUG_ON(!RB_EMPTY_NODE(&dl_se->rb_node));

        rb_add_cached(&dl_se->rb_node, &dl_rq->root, __dl_less);

        inc_dl_tasks(dl_se, dl_rq);
}

static void __dequeue_dl_entity(struct sched_dl_entity *dl_se)
{
        struct dl_rq *dl_rq = dl_rq_of_se(dl_se);

        if (RB_EMPTY_NODE(&dl_se->rb_node))
                return;

        rb_erase_cached(&dl_se->rb_node, &dl_rq->root);

        RB_CLEAR_NODE(&dl_se->rb_node);

        dec_dl_tasks(dl_se, dl_rq);
}

static void
enqueue_dl_entity(struct sched_dl_entity *dl_se, int flags)
{
        BUG_ON(on_dl_rq(dl_se));

        /*
         * If this is a wakeup or a new instance, the scheduling
         * parameters of the task might need updating. Otherwise,
         * we want a replenishment of its runtime.
         */
        if (flags & ENQUEUE_WAKEUP) {
                task_contending(dl_se, flags);
                update_dl_entity(dl_se);
        } else if (flags & ENQUEUE_REPLENISH) {
                replenish_dl_entity(dl_se);
        } else if ((flags & ENQUEUE_RESTORE) &&
                  dl_time_before(dl_se->deadline,
                                 rq_clock(rq_of_dl_rq(dl_rq_of_se(dl_se))))) {
                setup_new_dl_entity(dl_se);
        }

        __enqueue_dl_entity(dl_se);
}

static void dequeue_dl_entity(struct sched_dl_entity *dl_se)
{
        __dequeue_dl_entity(dl_se);
}

static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags)
{
        if (is_dl_boosted(&p->dl)) {
                /*
                 * Because of delays in the detection of the overrun of a
                 * thread's runtime, it might be the case that a thread
                 * goes to sleep in a rt mutex with negative runtime. As
                 * a consequence, the thread will be throttled.
                 *
                 * While waiting for the mutex, this thread can also be
                 * boosted via PI, resulting in a thread that is throttled
                 * and boosted at the same time.
                 *
                 * In this case, the boost overrides the throttle.
                 */
                if (p->dl.dl_throttled) {
                        /*
                         * The replenish timer needs to be canceled. No
                         * problem if it fires concurrently: boosted threads
                         * are ignored in dl_task_timer().
                         */
                        hrtimer_try_to_cancel(&p->dl.dl_timer);
                        p->dl.dl_throttled = 0;
                }
        } else if (!dl_prio(p->normal_prio)) {
                /*
                 * Special case in which we have a !SCHED_DEADLINE task that is going
                 * to be deboosted, but exceeds its runtime while doing so. No point in
                 * replenishing it, as it's going to return back to its original
                 * scheduling class after this. If it has been throttled, we need to
                 * clear the flag, otherwise the task may wake up as throttled after
                 * being boosted again with no means to replenish the runtime and clear
                 * the throttle.
                 */
                p->dl.dl_throttled = 0;
                BUG_ON(!is_dl_boosted(&p->dl) || flags != ENQUEUE_REPLENISH);
                return;
        }

        /*
         * Check if a constrained deadline task was activated
         * after the deadline but before the next period.
         * If that is the case, the task will be throttled and
         * the replenishment timer will be set to the next period.
         */
        if (!p->dl.dl_throttled && !dl_is_implicit(&p->dl))
                dl_check_constrained_dl(&p->dl);

        if (p->on_rq == TASK_ON_RQ_MIGRATING || flags & ENQUEUE_RESTORE) {
                add_rq_bw(&p->dl, &rq->dl);
                add_running_bw(&p->dl, &rq->dl);
        }

        /*
         * If p is throttled, we do not enqueue it. In fact, if it exhausted
         * its budget it needs a replenishment and, since it now is on
         * its rq, the bandwidth timer callback (which clearly has not
         * run yet) will take care of this.
         * However, the active utilization does not depend on the fact
         * that the task is on the runqueue or not (but depends on the
         * task's state - in GRUB parlance, "inactive" vs "active contending").
         * In other words, even if a task is throttled its utilization must
         * be counted in the active utilization; hence, we need to call
         * add_running_bw().
         */
        if (p->dl.dl_throttled && !(flags & ENQUEUE_REPLENISH)) {
                if (flags & ENQUEUE_WAKEUP)
                        task_contending(&p->dl, flags);

                return;
        }

        enqueue_dl_entity(&p->dl, flags);

        if (!task_current(rq, p) && p->nr_cpus_allowed > 1)
                enqueue_pushable_dl_task(rq, p);
}

static void __dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags)
{
        dequeue_dl_entity(&p->dl);
        dequeue_pushable_dl_task(rq, p);
}

static void dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags)
{
        update_curr_dl(rq);
        __dequeue_task_dl(rq, p, flags);

        if (p->on_rq == TASK_ON_RQ_MIGRATING || flags & DEQUEUE_SAVE) {
                sub_running_bw(&p->dl, &rq->dl);
                sub_rq_bw(&p->dl, &rq->dl);
        }

        /*
         * This check allows to start the inactive timer (or to immediately
         * decrease the active utilization, if needed) in two cases:
         * when the task blocks and when it is terminating
         * (p->state == TASK_DEAD). We can handle the two cases in the same
         * way, because from GRUB's point of view the same thing is happening
         * (the task moves from "active contending" to "active non contending"
         * or "inactive")
         */
        if (flags & DEQUEUE_SLEEP)
                task_non_contending(p);
}

/*
 * Yield task semantic for -deadline tasks is:
 *
 *   get off from the CPU until our next instance, with
 *   a new runtime. This is of little use now, since we
 *   don't have a bandwidth reclaiming mechanism. Anyway,
 *   bandwidth reclaiming is planned for the future, and
 *   yield_task_dl will indicate that some spare budget
 *   is available for other task instances to use it.
 */
static void yield_task_dl(struct rq *rq)
{
        /*
         * We make the task go to sleep until its current deadline by
         * forcing its runtime to zero. This way, update_curr_dl() stops
         * it and the bandwidth timer will wake it up and will give it
         * new scheduling parameters (thanks to dl_yielded=1).
         */
        rq->curr->dl.dl_yielded = 1;

        update_rq_clock(rq);
        update_curr_dl(rq);
        /*
         * Tell update_rq_clock() that we've just updated,
         * so we don't do microscopic update in schedule()
         * and double the fastpath cost.
         */
        rq_clock_skip_update(rq);
}

#ifdef CONFIG_SMP

static int find_later_rq(struct task_struct *task);

static int
select_task_rq_dl(struct task_struct *p, int cpu, int flags)
{
        struct task_struct *curr;
        bool select_rq;
        struct rq *rq;

        if (!(flags & WF_TTWU))
                goto out;

        rq = cpu_rq(cpu);

        rcu_read_lock();
        curr = READ_ONCE(rq->curr); /* unlocked access */

        /*
         * If we are dealing with a -deadline task, we must
         * decide where to wake it up.
         * If it has a later deadline and the current task
         * on this rq can't move (provided the waking task
         * can!) we prefer to send it somewhere else. On the
         * other hand, if it has a shorter deadline, we
         * try to make it stay here, it might be important.
         */
        select_rq = unlikely(dl_task(curr)) &&
                    (curr->nr_cpus_allowed < 2 ||
                     !dl_entity_preempt(&p->dl, &curr->dl)) &&
                    p->nr_cpus_allowed > 1;

        /*
         * Take the capacity of the CPU into account to
         * ensure it fits the requirement of the task.
         */
        if (static_branch_unlikely(&sched_asym_cpucapacity))
                select_rq |= !dl_task_fits_capacity(p, cpu);

        if (select_rq) {
                int target = find_later_rq(p);

                if (target != -1 &&
                                (dl_time_before(p->dl.deadline,
                                        cpu_rq(target)->dl.earliest_dl.curr) ||
                                (cpu_rq(target)->dl.dl_nr_running == 0)))
                        cpu = target;
        }
        rcu_read_unlock();

out:
        return cpu;
}

static void migrate_task_rq_dl(struct task_struct *p, int new_cpu __maybe_unused)
{
        struct rq *rq;

        if (READ_ONCE(p->__state) != TASK_WAKING)
                return;

        rq = task_rq(p);
        /*
         * Since p->state == TASK_WAKING, set_task_cpu() has been called
         * from try_to_wake_up(). Hence, p->pi_lock is locked, but
         * rq->lock is not... So, lock it
         */
        raw_spin_rq_lock(rq);
        if (p->dl.dl_non_contending) {
                sub_running_bw(&p->dl, &rq->dl);
                p->dl.dl_non_contending = 0;
                /*
                 * If the timer handler is currently running and the
                 * timer cannot be canceled, inactive_task_timer()
                 * will see that dl_not_contending is not set, and
                 * will not touch the rq's active utilization,
                 * so we are still safe.
                 */
                if (hrtimer_try_to_cancel(&p->dl.inactive_timer) == 1)
                        put_task_struct(p);
        }
        sub_rq_bw(&p->dl, &rq->dl);
        raw_spin_rq_unlock(rq);
}

static void check_preempt_equal_dl(struct rq *rq, struct task_struct *p)
{
        /*
         * Current can't be migrated, useless to reschedule,
         * let's hope p can move out.
         */
        if (rq->curr->nr_cpus_allowed == 1 ||
            !cpudl_find(&rq->rd->cpudl, rq->curr, NULL))
                return;

        /*
         * p is migratable, so let's not schedule it and
         * see if it is pushed or pulled somewhere else.
         */
        if (p->nr_cpus_allowed != 1 &&
            cpudl_find(&rq->rd->cpudl, p, NULL))
                return;

        resched_curr(rq);
}

static int balance_dl(struct rq *rq, struct task_struct *p, struct rq_flags *rf)
{
        if (!on_dl_rq(&p->dl) && need_pull_dl_task(rq, p)) {
                /*
                 * This is OK, because current is on_cpu, which avoids it being
                 * picked for load-balance and preemption/IRQs are still
                 * disabled avoiding further scheduler activity on it and we've
                 * not yet started the picking loop.
                 */
                rq_unpin_lock(rq, rf);
                pull_dl_task(rq);
                rq_repin_lock(rq, rf);
        }

        return sched_stop_runnable(rq) || sched_dl_runnable(rq);
}
#endif /* CONFIG_SMP */

/*
 * Only called when both the current and waking task are -deadline
 * tasks.
 */
static void check_preempt_curr_dl(struct rq *rq, struct task_struct *p,
                                  int flags)
{
        if (dl_entity_preempt(&p->dl, &rq->curr->dl)) {
                resched_curr(rq);
                return;
        }

#ifdef CONFIG_SMP
        /*
         * In the unlikely case current and p have the same deadline
         * let us try to decide what's the best thing to do...
         */
        if ((p->dl.deadline == rq->curr->dl.deadline) &&
            !test_tsk_need_resched(rq->curr))
                check_preempt_equal_dl(rq, p);
#endif /* CONFIG_SMP */
}

#ifdef CONFIG_SCHED_HRTICK
static void start_hrtick_dl(struct rq *rq, struct task_struct *p)
{
        hrtick_start(rq, p->dl.runtime);
}
#else /* !CONFIG_SCHED_HRTICK */
static void start_hrtick_dl(struct rq *rq, struct task_struct *p)
{
}
#endif

static void set_next_task_dl(struct rq *rq, struct task_struct *p, bool first)
{
        p->se.exec_start = rq_clock_task(rq);

        /* You can't push away the running task */
        dequeue_pushable_dl_task(rq, p);

        if (!first)
                return;

        if (hrtick_enabled_dl(rq))
                start_hrtick_dl(rq, p);

        if (rq->curr->sched_class != &dl_sched_class)
                update_dl_rq_load_avg(rq_clock_pelt(rq), rq, 0);

        deadline_queue_push_tasks(rq);
}

static struct sched_dl_entity *pick_next_dl_entity(struct rq *rq,
                                                   struct dl_rq *dl_rq)
{
        struct rb_node *left = rb_first_cached(&dl_rq->root);

        if (!left)
                return NULL;

        return rb_entry(left, struct sched_dl_entity, rb_node);
}

static struct task_struct *pick_task_dl(struct rq *rq)
{
        struct sched_dl_entity *dl_se;
        struct dl_rq *dl_rq = &rq->dl;
        struct task_struct *p;

        if (!sched_dl_runnable(rq))
                return NULL;

        dl_se = pick_next_dl_entity(rq, dl_rq);
        BUG_ON(!dl_se);
        p = dl_task_of(dl_se);

        return p;
}

static struct task_struct *pick_next_task_dl(struct rq *rq)
{
        struct task_struct *p;

        p = pick_task_dl(rq);
        if (p)
                set_next_task_dl(rq, p, true);

        return p;
}

static void put_prev_task_dl(struct rq *rq, struct task_struct *p)
{
        update_curr_dl(rq);

        update_dl_rq_load_avg(rq_clock_pelt(rq), rq, 1);
        if (on_dl_rq(&p->dl) && p->nr_cpus_allowed > 1)
                enqueue_pushable_dl_task(rq, p);
}

/*
 * scheduler tick hitting a task of our scheduling class.
 *
 * NOTE: This function can be called remotely by the tick offload that
 * goes along full dynticks. Therefore no local assumption can be made
 * and everything must be accessed through the @rq and @curr passed in
 * parameters.
 */
static void task_tick_dl(struct rq *rq, struct task_struct *p, int queued)
{
        update_curr_dl(rq);

        update_dl_rq_load_avg(rq_clock_pelt(rq), rq, 1);
        /*
         * Even when we have runtime, update_curr_dl() might have resulted in us
         * not being the leftmost task anymore. In that case NEED_RESCHED will
         * be set and schedule() will start a new hrtick for the next task.
         */
        if (hrtick_enabled_dl(rq) && queued && p->dl.runtime > 0 &&
            is_leftmost(p, &rq->dl))
                start_hrtick_dl(rq, p);
}

static void task_fork_dl(struct task_struct *p)
{
        /*
         * SCHED_DEADLINE tasks cannot fork and this is achieved through
         * sched_fork()
         */
}

#ifdef CONFIG_SMP

/* Only try algorithms three times */
#define DL_MAX_TRIES 3

static int pick_dl_task(struct rq *rq, struct task_struct *p, int cpu)
{
        if (!task_running(rq, p) &&
            cpumask_test_cpu(cpu, &p->cpus_mask))
                return 1;
        return 0;
}

/*
 * Return the earliest pushable rq's task, which is suitable to be executed
 * on the CPU, NULL otherwise:
 */
static struct task_struct *pick_earliest_pushable_dl_task(struct rq *rq, int cpu)
{
        struct rb_node *next_node = rq->dl.pushable_dl_tasks_root.rb_leftmost;
        struct task_struct *p = NULL;

        if (!has_pushable_dl_tasks(rq))
                return NULL;

next_node:
        if (next_node) {
                p = rb_entry(next_node, struct task_struct, pushable_dl_tasks);

                if (pick_dl_task(rq, p, cpu))
                        return p;

                next_node = rb_next(next_node);
                goto next_node;
        }

        return NULL;
}

static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl);

static int find_later_rq(struct task_struct *task)
{
        struct sched_domain *sd;
        struct cpumask *later_mask = this_cpu_cpumask_var_ptr(local_cpu_mask_dl);
        int this_cpu = smp_processor_id();
        int cpu = task_cpu(task);

        /* Make sure the mask is initialized first */
        if (unlikely(!later_mask))
                return -1;

        if (task->nr_cpus_allowed == 1)
                return -1;

        /*
         * We have to consider system topology and task affinity
         * first, then we can look for a suitable CPU.
         */
        if (!cpudl_find(&task_rq(task)->rd->cpudl, task, later_mask))
                return -1;

        /*
         * If we are here, some targets have been found, including
         * the most suitable which is, among the runqueues where the
         * current tasks have later deadlines than the task's one, the
         * rq with the latest possible one.
         *
         * Now we check how well this matches with task's
         * affinity and system topology.
         *
         * The last CPU where the task run is our first
         * guess, since it is most likely cache-hot there.
         */
        if (cpumask_test_cpu(cpu, later_mask))
                return cpu;
        /*
         * Check if this_cpu is to be skipped (i.e., it is
         * not in the mask) or not.
         */
        if (!cpumask_test_cpu(this_cpu, later_mask))
                this_cpu = -1;

        rcu_read_lock();
        for_each_domain(cpu, sd) {
                if (sd->flags & SD_WAKE_AFFINE) {
                        int best_cpu;

                        /*
                         * If possible, preempting this_cpu is
                         * cheaper than migrating.
                         */
                        if (this_cpu != -1 &&
                            cpumask_test_cpu(this_cpu, sched_domain_span(sd))) {
                                rcu_read_unlock();
                                return this_cpu;
                        }

                        best_cpu = cpumask_any_and_distribute(later_mask,
                                                              sched_domain_span(sd));
                        /*
                         * Last chance: if a CPU being in both later_mask
                         * and current sd span is valid, that becomes our
                         * choice. Of course, the latest possible CPU is
                         * already under consideration through later_mask.
                         */
                        if (best_cpu < nr_cpu_ids) {
                                rcu_read_unlock();
                                return best_cpu;
                        }
                }
        }
        rcu_read_unlock();

        /*
         * At this point, all our guesses failed, we just return
         * 'something', and let the caller sort the things out.
         */
        if (this_cpu != -1)
                return this_cpu;

        cpu = cpumask_any_distribute(later_mask);
        if (cpu < nr_cpu_ids)
                return cpu;

        return -1;
}

/* Locks the rq it finds */
static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq)
{
        struct rq *later_rq = NULL;
        int tries;
        int cpu;

        for (tries = 0; tries < DL_MAX_TRIES; tries++) {
                cpu = find_later_rq(task);

                if ((cpu == -1) || (cpu == rq->cpu))
                        break;

                later_rq = cpu_rq(cpu);

                if (later_rq->dl.dl_nr_running &&
                    !dl_time_before(task->dl.deadline,
                                        later_rq->dl.earliest_dl.curr)) {
                        /*
                         * Target rq has tasks of equal or earlier deadline,
                         * retrying does not release any lock and is unlikely
                         * to yield a different result.
                         */
                        later_rq = NULL;
                        break;
                }

                /* Retry if something changed. */
                if (double_lock_balance(rq, later_rq)) {
                        if (unlikely(task_rq(task) != rq ||
                                     !cpumask_test_cpu(later_rq->cpu, &task->cpus_mask) ||
                                     task_running(rq, task) ||
                                     !dl_task(task) ||
                                     !task_on_rq_queued(task))) {
                                double_unlock_balance(rq, later_rq);
                                later_rq = NULL;
                                break;
                        }
                }

                /*
                 * If the rq we found has no -deadline task, or
                 * its earliest one has a later deadline than our
                 * task, the rq is a good one.
                 */
                if (!later_rq->dl.dl_nr_running ||
                    dl_time_before(task->dl.deadline,
                                   later_rq->dl.earliest_dl.curr))
                        break;

                /* Otherwise we try again. */
                double_unlock_balance(rq, later_rq);
                later_rq = NULL;
        }

        return later_rq;
}

static struct task_struct *pick_next_pushable_dl_task(struct rq *rq)
{
        struct task_struct *p;

        if (!has_pushable_dl_tasks(rq))
                return NULL;

        p = rb_entry(rq->dl.pushable_dl_tasks_root.rb_leftmost,
                     struct task_struct, pushable_dl_tasks);

        BUG_ON(rq->cpu != task_cpu(p));
        BUG_ON(task_current(rq, p));
        BUG_ON(p->nr_cpus_allowed <= 1);

        BUG_ON(!task_on_rq_queued(p));
        BUG_ON(!dl_task(p));

        return p;
}

/*
 * See if the non running -deadline tasks on this rq
 * can be sent to some other CPU where they can preempt
 * and start executing.
 */
static int push_dl_task(struct rq *rq)
{
        struct task_struct *next_task;
        struct rq *later_rq;
        int ret = 0;

        if (!rq->dl.overloaded)
                return 0;

        next_task = pick_next_pushable_dl_task(rq);
        if (!next_task)
                return 0;

retry:
        if (is_migration_disabled(next_task))
                return 0;

        if (WARN_ON(next_task == rq->curr))
                return 0;

        /*
         * If next_task preempts rq->curr, and rq->curr
         * can move away, it makes sense to just reschedule
         * without going further in pushing next_task.
         */
        if (dl_task(rq->curr) &&
            dl_time_before(next_task->dl.deadline, rq->curr->dl.deadline) &&
            rq->curr->nr_cpus_allowed > 1) {
                resched_curr(rq);
                return 0;
        }

        /* We might release rq lock */
        get_task_struct(next_task);

        /* Will lock the rq it'll find */
        later_rq = find_lock_later_rq(next_task, rq);
        if (!later_rq) {
                struct task_struct *task;

                /*
                 * We must check all this again, since
                 * find_lock_later_rq releases rq->lock and it is
                 * then possible that next_task has migrated.
                 */
                task = pick_next_pushable_dl_task(rq);
                if (task == next_task) {
                        /*
                         * The task is still there. We don't try
                         * again, some other CPU will pull it when ready.
                         */
                        goto out;
                }

                if (!task)
                        /* No more tasks */
                        goto out;

                put_task_struct(next_task);
                next_task = task;
                goto retry;
        }

        deactivate_task(rq, next_task, 0);
        set_task_cpu(next_task, later_rq->cpu);

        /*
         * Update the later_rq clock here, because the clock is used
         * by the cpufreq_update_util() inside __add_running_bw().
         */
        update_rq_clock(later_rq);
        activate_task(later_rq, next_task, ENQUEUE_NOCLOCK);
        ret = 1;

        resched_curr(later_rq);

        double_unlock_balance(rq, later_rq);

out:
        put_task_struct(next_task);

        return ret;
}

static void push_dl_tasks(struct rq *rq)
{
        /* push_dl_task() will return true if it moved a -deadline task */
        while (push_dl_task(rq))
                ;
}

static void pull_dl_task(struct rq *this_rq)
{
        int this_cpu = this_rq->cpu, cpu;
        struct task_struct *p, *push_task;
        bool resched = false;
        struct rq *src_rq;
        u64 dmin = LONG_MAX;

        if (likely(!dl_overloaded(this_rq)))
                return;

        /*
         * Match the barrier from dl_set_overloaded; this guarantees that if we
         * see overloaded we must also see the dlo_mask bit.
         */
        smp_rmb();

        for_each_cpu(cpu, this_rq->rd->dlo_mask) {
                if (this_cpu == cpu)
                        continue;

                src_rq = cpu_rq(cpu);

                /*
                 * It looks racy, abd it is! However, as in sched_rt.c,
                 * we are fine with this.
                 */
                if (this_rq->dl.dl_nr_running &&
                    dl_time_before(this_rq->dl.earliest_dl.curr,
                                   src_rq->dl.earliest_dl.next))
                        continue;

                /* Might drop this_rq->lock */
                push_task = NULL;
                double_lock_balance(this_rq, src_rq);

                /*
                 * If there are no more pullable tasks on the
                 * rq, we're done with it.
                 */
                if (src_rq->dl.dl_nr_running <= 1)
                        goto skip;

                p = pick_earliest_pushable_dl_task(src_rq, this_cpu);

                /*
                 * We found a task to be pulled if:
                 *  - it preempts our current (if there's one),
                 *  - it will preempt the last one we pulled (if any).
                 */
                if (p && dl_time_before(p->dl.deadline, dmin) &&
                    (!this_rq->dl.dl_nr_running ||
                     dl_time_before(p->dl.deadline,
                                    this_rq->dl.earliest_dl.curr))) {
                        WARN_ON(p == src_rq->curr);
                        WARN_ON(!task_on_rq_queued(p));

                        /*
                         * Then we pull iff p has actually an earlier
                         * deadline than the current task of its runqueue.
                         */
                        if (dl_time_before(p->dl.deadline,
                                           src_rq->curr->dl.deadline))
                                goto skip;

                        if (is_migration_disabled(p)) {
                                push_task = get_push_task(src_rq);
                        } else {
                                deactivate_task(src_rq, p, 0);
                                set_task_cpu(p, this_cpu);
                                activate_task(this_rq, p, 0);
                                dmin = p->dl.deadline;
                                resched = true;
                        }

                        /* Is there any other task even earlier? */
                }
skip:
                double_unlock_balance(this_rq, src_rq);

                if (push_task) {
                        raw_spin_rq_unlock(this_rq);
                        stop_one_cpu_nowait(src_rq->cpu, push_cpu_stop,
                                            push_task, &src_rq->push_work);
                        raw_spin_rq_lock(this_rq);
                }
        }

        if (resched)
                resched_curr(this_rq);
}

/*
 * Since the task is not running and a reschedule is not going to happen
 * anytime soon on its runqueue, we try pushing it away now.
 */
static void task_woken_dl(struct rq *rq, struct task_struct *p)
{
        if (!task_running(rq, p) &&
            !test_tsk_need_resched(rq->curr) &&
            p->nr_cpus_allowed > 1 &&
            dl_task(rq->curr) &&
            (rq->curr->nr_cpus_allowed < 2 ||
             !dl_entity_preempt(&p->dl, &rq->curr->dl))) {
                push_dl_tasks(rq);
        }
}

static void set_cpus_allowed_dl(struct task_struct *p,
                                const struct cpumask *new_mask,
                                u32 flags)
{
        struct root_domain *src_rd;
        struct rq *rq;

        BUG_ON(!dl_task(p));

        rq = task_rq(p);
        src_rd = rq->rd;
        /*
         * Migrating a SCHED_DEADLINE task between exclusive
         * cpusets (different root_domains) entails a bandwidth
         * update. We already made space for us in the destination
         * domain (see cpuset_can_attach()).
         */
        if (!cpumask_intersects(src_rd->span, new_mask)) {
                struct dl_bw *src_dl_b;

                src_dl_b = dl_bw_of(cpu_of(rq));
                /*
                 * We now free resources of the root_domain we are migrating
                 * off. In the worst case, sched_setattr() may temporary fail
                 * until we complete the update.
                 */
                raw_spin_lock(&src_dl_b->lock);
                __dl_sub(src_dl_b, p->dl.dl_bw, dl_bw_cpus(task_cpu(p)));
                raw_spin_unlock(&src_dl_b->lock);
        }

        set_cpus_allowed_common(p, new_mask, flags);
}

/* Assumes rq->lock is held */
static void rq_online_dl(struct rq *rq)
{
        if (rq->dl.overloaded)
                dl_set_overload(rq);

        cpudl_set_freecpu(&rq->rd->cpudl, rq->cpu);
        if (rq->dl.dl_nr_running > 0)
                cpudl_set(&rq->rd->cpudl, rq->cpu, rq->dl.earliest_dl.curr);
}

/* Assumes rq->lock is held */
static void rq_offline_dl(struct rq *rq)
{
        if (rq->dl.overloaded)
                dl_clear_overload(rq);

        cpudl_clear(&rq->rd->cpudl, rq->cpu);
        cpudl_clear_freecpu(&rq->rd->cpudl, rq->cpu);
}

void __init init_sched_dl_class(void)
{
        unsigned int i;

        for_each_possible_cpu(i)
                zalloc_cpumask_var_node(&per_cpu(local_cpu_mask_dl, i),
                                        GFP_KERNEL, cpu_to_node(i));
}

void dl_add_task_root_domain(struct task_struct *p)
{
        struct rq_flags rf;
        struct rq *rq;
        struct dl_bw *dl_b;

        raw_spin_lock_irqsave(&p->pi_lock, rf.flags);
        if (!dl_task(p)) {
                raw_spin_unlock_irqrestore(&p->pi_lock, rf.flags);
                return;
        }

        rq = __task_rq_lock(p, &rf);

        dl_b = &rq->rd->dl_bw;
        raw_spin_lock(&dl_b->lock);

        __dl_add(dl_b, p->dl.dl_bw, cpumask_weight(rq->rd->span));

        raw_spin_unlock(&dl_b->lock);

        task_rq_unlock(rq, p, &rf);
}

void dl_clear_root_domain(struct root_domain *rd)
{
        unsigned long flags;

        raw_spin_lock_irqsave(&rd->dl_bw.lock, flags);
        rd->dl_bw.total_bw = 0;
        raw_spin_unlock_irqrestore(&rd->dl_bw.lock, flags);
}

#endif /* CONFIG_SMP */

static void switched_from_dl(struct rq *rq, struct task_struct *p)
{
        /*
         * task_non_contending() can start the "inactive timer" (if the 0-lag
         * time is in the future). If the task switches back to dl before
         * the "inactive timer" fires, it can continue to consume its current
         * runtime using its current deadline. If it stays outside of
         * SCHED_DEADLINE until the 0-lag time passes, inactive_task_timer()
         * will reset the task parameters.
         */
        if (task_on_rq_queued(p) && p->dl.dl_runtime)
                task_non_contending(p);

        if (!task_on_rq_queued(p)) {
                /*
                 * Inactive timer is armed. However, p is leaving DEADLINE and
                 * might migrate away from this rq while continuing to run on
                 * some other class. We need to remove its contribution from
                 * this rq running_bw now, or sub_rq_bw (below) will complain.
                 */
                if (p->dl.dl_non_contending)
                        sub_running_bw(&p->dl, &rq->dl);
                sub_rq_bw(&p->dl, &rq->dl);
        }

        /*
         * We cannot use inactive_task_timer() to invoke sub_running_bw()
         * at the 0-lag time, because the task could have been migrated
         * while SCHED_OTHER in the meanwhile.
         */
        if (p->dl.dl_non_contending)
                p->dl.dl_non_contending = 0;

        /*
         * Since this might be the only -deadline task on the rq,
         * this is the right place to try to pull some other one
         * from an overloaded CPU, if any.
         */
        if (!task_on_rq_queued(p) || rq->dl.dl_nr_running)
                return;

        deadline_queue_pull_task(rq);
}

/*
 * When switching to -deadline, we may overload the rq, then
 * we try to push someone off, if possible.
 */
static void switched_to_dl(struct rq *rq, struct task_struct *p)
{
        if (hrtimer_try_to_cancel(&p->dl.inactive_timer) == 1)
                put_task_struct(p);

        /* If p is not queued we will update its parameters at next wakeup. */
        if (!task_on_rq_queued(p)) {
                add_rq_bw(&p->dl, &rq->dl);

                return;
        }

        if (rq->curr != p) {
#ifdef CONFIG_SMP
                if (p->nr_cpus_allowed > 1 && rq->dl.overloaded)
                        deadline_queue_push_tasks(rq);
#endif
                if (dl_task(rq->curr))
                        check_preempt_curr_dl(rq, p, 0);
                else
                        resched_curr(rq);
        } else {
                update_dl_rq_load_avg(rq_clock_pelt(rq), rq, 0);
        }
}

/*
 * If the scheduling parameters of a -deadline task changed,
 * a push or pull operation might be needed.
 */
static void prio_changed_dl(struct rq *rq, struct task_struct *p,
                            int oldprio)
{
        if (task_on_rq_queued(p) || task_current(rq, p)) {
#ifdef CONFIG_SMP
                /*
                 * This might be too much, but unfortunately
                 * we don't have the old deadline value, and
                 * we can't argue if the task is increasing
                 * or lowering its prio, so...
                 */
                if (!rq->dl.overloaded)
                        deadline_queue_pull_task(rq);

                /*
                 * If we now have a earlier deadline task than p,
                 * then reschedule, provided p is still on this
                 * runqueue.
                 */
                if (dl_time_before(rq->dl.earliest_dl.curr, p->dl.deadline))
                        resched_curr(rq);
#else
                /*
                 * Again, we don't know if p has a earlier
                 * or later deadline, so let's blindly set a
                 * (maybe not needed) rescheduling point.
                 */
                resched_curr(rq);
#endif /* CONFIG_SMP */
        }
}

DEFINE_SCHED_CLASS(dl) = {

        .enqueue_task           = enqueue_task_dl,
        .dequeue_task           = dequeue_task_dl,
        .yield_task             = yield_task_dl,

        .check_preempt_curr     = check_preempt_curr_dl,

        .pick_next_task         = pick_next_task_dl,
        .put_prev_task          = put_prev_task_dl,
        .set_next_task          = set_next_task_dl,

#ifdef CONFIG_SMP
        .balance                = balance_dl,
        .pick_task              = pick_task_dl,
        .select_task_rq         = select_task_rq_dl,
        .migrate_task_rq        = migrate_task_rq_dl,
        .set_cpus_allowed       = set_cpus_allowed_dl,
        .rq_online              = rq_online_dl,
        .rq_offline             = rq_offline_dl,
        .task_woken             = task_woken_dl,
        .find_lock_rq           = find_lock_later_rq,
#endif

        .task_tick              = task_tick_dl,
        .task_fork              = task_fork_dl,

        .prio_changed           = prio_changed_dl,
        .switched_from          = switched_from_dl,
        .switched_to            = switched_to_dl,

        .update_curr            = update_curr_dl,
};

/* Used for dl_bw check and update, used under sched_rt_handler()::mutex */
static u64 dl_generation;

int sched_dl_global_validate(void)
{
        u64 runtime = global_rt_runtime();
        u64 period = global_rt_period();
        u64 new_bw = to_ratio(period, runtime);
        u64 gen = ++dl_generation;
        struct dl_bw *dl_b;
        int cpu, cpus, ret = 0;
        unsigned long flags;

        /*
         * Here we want to check the bandwidth not being set to some
         * value smaller than the currently allocated bandwidth in
         * any of the root_domains.
         */
        for_each_possible_cpu(cpu) {
                rcu_read_lock_sched();

                if (dl_bw_visited(cpu, gen))
                        goto next;

                dl_b = dl_bw_of(cpu);
                cpus = dl_bw_cpus(cpu);

                raw_spin_lock_irqsave(&dl_b->lock, flags);
                if (new_bw * cpus < dl_b->total_bw)
                        ret = -EBUSY;
                raw_spin_unlock_irqrestore(&dl_b->lock, flags);

next:
                rcu_read_unlock_sched();

                if (ret)
                        break;
        }

        return ret;
}

static void init_dl_rq_bw_ratio(struct dl_rq *dl_rq)
{
        if (global_rt_runtime() == RUNTIME_INF) {
                dl_rq->bw_ratio = 1 << RATIO_SHIFT;
                dl_rq->extra_bw = 1 << BW_SHIFT;
        } else {
                dl_rq->bw_ratio = to_ratio(global_rt_runtime(),
                          global_rt_period()) >> (BW_SHIFT - RATIO_SHIFT);
                dl_rq->extra_bw = to_ratio(global_rt_period(),
                                                    global_rt_runtime());
        }
}

void sched_dl_do_global(void)
{
        u64 new_bw = -1;
        u64 gen = ++dl_generation;
        struct dl_bw *dl_b;
        int cpu;
        unsigned long flags;

        def_dl_bandwidth.dl_period = global_rt_period();
        def_dl_bandwidth.dl_runtime = global_rt_runtime();

        if (global_rt_runtime() != RUNTIME_INF)
                new_bw = to_ratio(global_rt_period(), global_rt_runtime());

        for_each_possible_cpu(cpu) {
                rcu_read_lock_sched();

                if (dl_bw_visited(cpu, gen)) {
                        rcu_read_unlock_sched();
                        continue;
                }

                dl_b = dl_bw_of(cpu);

                raw_spin_lock_irqsave(&dl_b->lock, flags);
                dl_b->bw = new_bw;
                raw_spin_unlock_irqrestore(&dl_b->lock, flags);

                rcu_read_unlock_sched();
                init_dl_rq_bw_ratio(&cpu_rq(cpu)->dl);
        }
}

/*
 * We must be sure that accepting a new task (or allowing changing the
 * parameters of an existing one) is consistent with the bandwidth
 * constraints. If yes, this function also accordingly updates the currently
 * allocated bandwidth to reflect the new situation.
 *
 * This function is called while holding p's rq->lock.
 */
int sched_dl_overflow(struct task_struct *p, int policy,
                      const struct sched_attr *attr)
{
        u64 period = attr->sched_period ?: attr->sched_deadline;
        u64 runtime = attr->sched_runtime;
        u64 new_bw = dl_policy(policy) ? to_ratio(period, runtime) : 0;
        int cpus, err = -1, cpu = task_cpu(p);
        struct dl_bw *dl_b = dl_bw_of(cpu);
        unsigned long cap;

        if (attr->sched_flags & SCHED_FLAG_SUGOV)
                return 0;

        /* !deadline task may carry old deadline bandwidth */
        if (new_bw == p->dl.dl_bw && task_has_dl_policy(p))
                return 0;

        /*
         * Either if a task, enters, leave, or stays -deadline but changes
         * its parameters, we may need to update accordingly the total
         * allocated bandwidth of the container.
         */
        raw_spin_lock(&dl_b->lock);
        cpus = dl_bw_cpus(cpu);
        cap = dl_bw_capacity(cpu);

        if (dl_policy(policy) && !task_has_dl_policy(p) &&
            !__dl_overflow(dl_b, cap, 0, new_bw)) {
                if (hrtimer_active(&p->dl.inactive_timer))
                        __dl_sub(dl_b, p->dl.dl_bw, cpus);
                __dl_add(dl_b, new_bw, cpus);
                err = 0;
        } else if (dl_policy(policy) && task_has_dl_policy(p) &&
                   !__dl_overflow(dl_b, cap, p->dl.dl_bw, new_bw)) {
                /*
                 * XXX this is slightly incorrect: when the task
                 * utilization decreases, we should delay the total
                 * utilization change until the task's 0-lag point.
                 * But this would require to set the task's "inactive
                 * timer" when the task is not inactive.
                 */
                __dl_sub(dl_b, p->dl.dl_bw, cpus);
                __dl_add(dl_b, new_bw, cpus);
                dl_change_utilization(p, new_bw);
                err = 0;
        } else if (!dl_policy(policy) && task_has_dl_policy(p)) {
                /*
                 * Do not decrease the total deadline utilization here,
                 * switched_from_dl() will take care to do it at the correct
                 * (0-lag) time.
                 */
                err = 0;
        }
        raw_spin_unlock(&dl_b->lock);

        return err;
}

/*
 * This function initializes the sched_dl_entity of a newly becoming
 * SCHED_DEADLINE task.
 *
 * Only the static values are considered here, the actual runtime and the
 * absolute deadline will be properly calculated when the task is enqueued
 * for the first time with its new policy.
 */
void __setparam_dl(struct task_struct *p, const struct sched_attr *attr)
{
        struct sched_dl_entity *dl_se = &p->dl;

        dl_se->dl_runtime = attr->sched_runtime;
        dl_se->dl_deadline = attr->sched_deadline;
        dl_se->dl_period = attr->sched_period ?: dl_se->dl_deadline;
        dl_se->flags = attr->sched_flags;
        dl_se->dl_bw = to_ratio(dl_se->dl_period, dl_se->dl_runtime);
        dl_se->dl_density = to_ratio(dl_se->dl_deadline, dl_se->dl_runtime);
}

void __getparam_dl(struct task_struct *p, struct sched_attr *attr)
{
        struct sched_dl_entity *dl_se = &p->dl;

        attr->sched_priority = p->rt_priority;
        attr->sched_runtime = dl_se->dl_runtime;
        attr->sched_deadline = dl_se->dl_deadline;
        attr->sched_period = dl_se->dl_period;
        attr->sched_flags = dl_se->flags;
}

/*
 * Default limits for DL period; on the top end we guard against small util
 * tasks still getting ridiculously long effective runtimes, on the bottom end we
 * guard against timer DoS.
 */
unsigned int sysctl_sched_dl_period_max = 1 << 22; /* ~4 seconds */
unsigned int sysctl_sched_dl_period_min = 100;     /* 100 us */

/*
 * This function validates the new parameters of a -deadline task.
 * We ask for the deadline not being zero, and greater or equal
 * than the runtime, as well as the period of being zero or
 * greater than deadline. Furthermore, we have to be sure that
 * user parameters are above the internal resolution of 1us (we
 * check sched_runtime only since it is always the smaller one) and
 * below 2^63 ns (we have to check both sched_deadline and
 * sched_period, as the latter can be zero).
 */
bool __checkparam_dl(const struct sched_attr *attr)
{
        u64 period, max, min;

        /* special dl tasks don't actually use any parameter */
        if (attr->sched_flags & SCHED_FLAG_SUGOV)
                return true;

        /* deadline != 0 */
        if (attr->sched_deadline == 0)
                return false;

        /*
         * Since we truncate DL_SCALE bits, make sure we're at least
         * that big.
         */
        if (attr->sched_runtime < (1ULL << DL_SCALE))
                return false;

        /*
         * Since we use the MSB for wrap-around and sign issues, make
         * sure it's not set (mind that period can be equal to zero).
         */
        if (attr->sched_deadline & (1ULL << 63) ||
            attr->sched_period & (1ULL << 63))
                return false;

        period = attr->sched_period;
        if (!period)
                period = attr->sched_deadline;

        /* runtime <= deadline <= period (if period != 0) */
        if (period < attr->sched_deadline ||
            attr->sched_deadline < attr->sched_runtime)
                return false;

        max = (u64)READ_ONCE(sysctl_sched_dl_period_max) * NSEC_PER_USEC;
        min = (u64)READ_ONCE(sysctl_sched_dl_period_min) * NSEC_PER_USEC;

        if (period < min || period > max)
                return false;

        return true;
}

/*
 * This function clears the sched_dl_entity static params.
 */
void __dl_clear_params(struct task_struct *p)
{
        struct sched_dl_entity *dl_se = &p->dl;

        dl_se->dl_runtime               = 0;
        dl_se->dl_deadline              = 0;
        dl_se->dl_period                = 0;
        dl_se->flags                    = 0;
        dl_se->dl_bw                    = 0;
        dl_se->dl_density               = 0;

        dl_se->dl_throttled             = 0;
        dl_se->dl_yielded               = 0;
        dl_se->dl_non_contending        = 0;
        dl_se->dl_overrun               = 0;

#ifdef CONFIG_RT_MUTEXES
        dl_se->pi_se                    = dl_se;
#endif
}

bool dl_param_changed(struct task_struct *p, const struct sched_attr *attr)
{
        struct sched_dl_entity *dl_se = &p->dl;

        if (dl_se->dl_runtime != attr->sched_runtime ||
            dl_se->dl_deadline != attr->sched_deadline ||
            dl_se->dl_period != attr->sched_period ||
            dl_se->flags != attr->sched_flags)
                return true;

        return false;
}

#ifdef CONFIG_SMP
int dl_task_can_attach(struct task_struct *p, const struct cpumask *cs_cpus_allowed)
{
        unsigned long flags, cap;
        unsigned int dest_cpu;
        struct dl_bw *dl_b;
        bool overflow;
        int ret;

        dest_cpu = cpumask_any_and(cpu_active_mask, cs_cpus_allowed);

        rcu_read_lock_sched();
        dl_b = dl_bw_of(dest_cpu);
        raw_spin_lock_irqsave(&dl_b->lock, flags);
        cap = dl_bw_capacity(dest_cpu);
        overflow = __dl_overflow(dl_b, cap, 0, p->dl.dl_bw);
        if (overflow) {
                ret = -EBUSY;
        } else {
                /*
                 * We reserve space for this task in the destination
                 * root_domain, as we can't fail after this point.
                 * We will free resources in the source root_domain
                 * later on (see set_cpus_allowed_dl()).
                 */
                int cpus = dl_bw_cpus(dest_cpu);

                __dl_add(dl_b, p->dl.dl_bw, cpus);
                ret = 0;
        }
        raw_spin_unlock_irqrestore(&dl_b->lock, flags);
        rcu_read_unlock_sched();

        return ret;
}

int dl_cpuset_cpumask_can_shrink(const struct cpumask *cur,
                                 const struct cpumask *trial)
{
        int ret = 1, trial_cpus;
        struct dl_bw *cur_dl_b;
        unsigned long flags;

        rcu_read_lock_sched();
        cur_dl_b = dl_bw_of(cpumask_any(cur));
        trial_cpus = cpumask_weight(trial);

        raw_spin_lock_irqsave(&cur_dl_b->lock, flags);
        if (cur_dl_b->bw != -1 &&
            cur_dl_b->bw * trial_cpus < cur_dl_b->total_bw)
                ret = 0;
        raw_spin_unlock_irqrestore(&cur_dl_b->lock, flags);
        rcu_read_unlock_sched();

        return ret;
}

bool dl_cpu_busy(unsigned int cpu)
{
        unsigned long flags, cap;
        struct dl_bw *dl_b;
        bool overflow;

        rcu_read_lock_sched();
        dl_b = dl_bw_of(cpu);
        raw_spin_lock_irqsave(&dl_b->lock, flags);
        cap = dl_bw_capacity(cpu);
        overflow = __dl_overflow(dl_b, cap, 0, 0);
        raw_spin_unlock_irqrestore(&dl_b->lock, flags);
        rcu_read_unlock_sched();

        return overflow;
}
#endif

#ifdef CONFIG_SCHED_DEBUG
void print_dl_stats(struct seq_file *m, int cpu)
{
        print_dl_rq(m, cpu, &cpu_rq(cpu)->dl);
}
#endif /* CONFIG_SCHED_DEBUG */